Implement SPCI_RX_RELEASE to replace hf_mailbox_clear.

Bug: 132421502
Change-Id: I63ffcce9b998ef98ff7ec3cdef41415a56a91b9f
diff --git a/src/arch/aarch64/hypervisor/handler.c b/src/arch/aarch64/hypervisor/handler.c
index 1125dcf..cf98bdb 100644
--- a/src/arch/aarch64/hypervisor/handler.c
+++ b/src/arch/aarch64/hypervisor/handler.c
@@ -324,6 +324,9 @@
 	case SPCI_FEATURES_32:
 		*args = api_spci_features(args->arg1);
 		return true;
+	case SPCI_RX_RELEASE_32:
+		*args = api_spci_rx_release(current(), next);
+		return true;
 	case SPCI_YIELD_32:
 		api_yield(current(), next);
 
@@ -450,10 +453,6 @@
 			ipa_init(args.arg1), ipa_init(args.arg2), vcpu, &next);
 		break;
 
-	case HF_MAILBOX_CLEAR:
-		vcpu->regs.r[0] = api_mailbox_clear(vcpu, &next);
-		break;
-
 	case HF_MAILBOX_WRITABLE_GET:
 		vcpu->regs.r[0] = api_mailbox_writable_get(vcpu);
 		break;